Conventional passive vehicle suspensions employ a spring and shock absorber to isolate body motion from wheel motion. Advances have been made in suspensions by making the suspensions semi or fully active. For example, in fully active suspension systems, a controlled force can be introduced by an actuator, such as an electromagnetic actuator, located between the sprung mass of the vehicle (i.e., the vehicle body) and an unsprung mass of the vehicle (i.e., a wheel assembly) to further minimize disturbances conducted from the interaction of the wheels with the road into the car body.
Conventional vehicles can utilize a variety of electrically controlled active suspension systems. An active suspension system includes an actuator system having a pair of rotary motors disposed on opposing ends of an output shaft and a transmission assembly associated with each of the rotary motors. The transmission assembly converts the rotation of the pair of rotary motors to a linear motion of the output shaft along a single direction.
The transmission assembly of each rotary motor is typically configured as a ball nut that engages a corresponding threaded portion of the output shaft. Conventional rotary motors include a motor housing having a stator and a rotor disposed therein with the ball nut being integrally machined as part of the rotor. Because the ball nut is a relatively high-precision component, in such a configuration, a manufacturer is required to grind the rotor and ball nut from a single piece of hardened material. The integrally-formed ball nut then can engage the output shaft via a set of balls disposed between the ball nut and the output shaft.